1. Field of the Invention
The invention relates to data collection and simulation of radio signals.
2. Description of the Related Art
A radio device can be tested against a radio channel either in a real environment or in a simulator simulating the real environment. A typical real measurement takes samples of a desired band about once a second, for example, when moving in an existing radio system. Real measurements are made for several reasons, such as optimizing and debugging the system, testing equipments and applications, verifying quality of service and collecting data on signals. However, tests conducted in a real radio system are undesirable and difficult, because tests taking place outdoors are affected by the weather and season, for example, that change all the time. In addition, a test conducted in one environment (city A) does not fully apply to a corresponding second environment (city B). Additionally, two consecutive tests in one environment are not exactly the same. It is also usually not possible to test a predetermined situation in a real environment. Some interesting phenomena may also take place so seldom in reality that they are hard to test even once not to mention repeatedly.
Then again with a device simulating a radio channel, it is possible to very freely simulate a desired type of radio channel. In a digital radio channel simulator, the channel may be modeled by a FIR (Finite Impulse Response) filter that forms a convolution between an estimated impulse response of a channel and desired radio frequency signal in such a manner that the data delayed by different delays is weighted by channel coefficients, i.e. tap coefficients, and the weighted data components are summed up. The channel coefficients can be altered to reflect the behavior of an actual channel.
Problems are, however, associated with both of the tests. Tests in real environments are too inaccurate, for example, for fast fading and they do not take into account interference and signals outside the designed band. Using a device simulating a radio channel, the impulse response model and the electromagnetic environment are predefined. The selected environment may be a “typical urban” area, for example, and that is the same for Paris and London although the cities are actually different. Additionally, a simulator can generate only artificial noise and interference to the channel, which differ essentially from real noise and interference of a radio system. Hence, there is a need for further development in simulation.